Map goes blanks when zooming in

I tried using the code with some shape files for Clay county and everything works perfectly.
Then I tried using the same code but with shape files from Dallas and the original image is displayed just fine but when I try to zoom in or pan around the image goes blank. I stepped through the code but didn't see any exceptions being thrown anywhere so not
sure what is going on. Just wondering if anyone has had this issue and could point me in the right direction.